The invention relates to a high-pressure discharge lamp having an elongate discharge vessel provided with an external ignition antenna which is formed from a thin spiralised wire which extends mainly alongside the discharge vessel and which lies against the discharge vessel in the cold state of the lamp and is fixed with one end to a support member.
A lamp of the kind described in the opening paragraph is widely used in, for example, public lighting. The known lamp, in which the discharge vessel is filled with sodium, mercury and rare gas is an efficient light source. The discharge vessel is provided with sealing constructions on either side. Each sealing construction comprises an electrically conducting lead-through element which is internally provided with a main electrode and which is externally electrically connected to a current supply conductor of the lamp. In the known lamp, the external ignition antenna is fixed to a support strip which supports a lead-through element of the discharge vessel on a current supply conductor and which at the same time provides the electric connection between the rigid supply conductor and the lead-through element of the discharge vessel.
The portion of the external antenna between the fixing point on the support strip and the portion lying alongside the discharge vessel is, in the known lamp, provided with a fixed mandril and is so bent away from the longitudinal axis of the discharge vessel that the fixing point is situated immediately next to the discharge vessel. The fixed mandril serves to give the bent-away portion sufficient rigidity so that the portion lying alongside the discharge vessel remains correctly positioned.
In the known lamp, practical problems occur with the construction of the external ignition antenna. Owing to the great heat load, the thin spiral is found to show plastic deformation, so that sagging of the ignition antenna starts to occur as early as after a working life of a few hundred hours. Sagging results in that the external ignition antenna no longer lies securely against the discharge vessel in the cold state of the lamp, which is disadvantageous for a good lamp ignition.
A further disadvantage of the known construction is that both the position of the fixing point on the support strip of the end and the positioning of the ignition antenna alongside the discharge vessel have to be fairly accurate, inter alia as a result of the rigid mandril.